The uptake and accumulation of polycyclic aromatic hydrocarbons (PAHs) in crops have gained much attention due to their toxicity to humans. Nitrogen (N) is an essential element for plant growth and has also been implicated in the acquisition and acropetal translocation of PAHs. OsNRT2 . 3b encodes a nitrate (NO 3 − ) transporter that is involved in the acquisition and mobilization of N in rice. Here, we investigated whether overexpression of OsNRT2 . 3b would exert any mitigating influence on the uptake and translocation of phenanthrene (Phe, a model PAH) in transgenic rice ( Oryza sativa ). The wild-type seedlings exhibited a reduction in plant height, primary root length, and shoot biomass when grown hydroponically in a medium supplemented with Phe. Acquisition of Phe by the roots and its subsequent translocation to shoots increased concomitantly with an increase in Phe concentration in the medium and duration of the treatment. OsNRT2 . 3b -overexpressing lines (Ox-6 and Ox-8) were generated independently. Compared with the wild-type, the concentration of Phe in Ox-6 and Ox-8 were significantly lower in the roots (47%–54%) and shoots (22%–31%) grown hydroponically with Phe (1 mg/L). Further, the wild-type and Ox lines were grown to maturity in a pot soil under Phe conditions and the concentrations of Phe and total N were assayed in the culms and flag leaves. Compared with the wild-type, in Ox lines the concentration of total N significantly increased in the culms (288%–366%) and flag leaves (12%–25%), while that of Phe significantly reduced in the culms (25%–28%) and flag leaves (18%–21%). The results revealed an antagonistic correlation between the concentration of total N and Phe. The concentration of Phe was also significantly lower (29%–38%) in the seeds of Ox lines than the wild-type. The study highlighted the efficacy of overexpressing OsNRT2 . 3b in mitigating the Phe toxicity by attenuating its acquisition, mobilization, and allocation to the seeds.
Minimizing the accumulation of polycyclic aromatic hydrocarbons (PAHs) in crops is crucial for human health. While OsNRT2.3b overexpression reduced phenanthrene (Phe) in rice, the underlying mechanisms and its response to complex conditions remained unclear. This study first confirmed a negative correlation between OsNRT2.3b expression and Phe utilizing 16 varieties. Further, to investigate whether the pH-sensing site H167 of OsNRT2.3b is the key, the wild-type (WT), OsNRT2.3b -overexpression (Ox), and H167-mutated OsNRT2.3b overexpression (H167R) were employed to expose to Phe under different nitrogen (N) and pH. Individual N and pH experiments demonstrated that H167 played a decisive role in suppressing Phe, with Phe in H167R being significantly higher than Ox. Moreover, both -N compared to + N, and pH 4.0 compared to 7.0, increased Phe while simultaneously enhancing H167-mediated regulation. Phe in Ox was significantly lower than H167R by 24.6% (-N) and 22.3% (pH 4.0). Combined pH and N treatments revealed that H167 was most effective under acidic and N-deficient conditions. Under hydroponic pH 4.0 & -N and pot soil pH 5.4 & LN, Phe in the roots of Ox were 19.7% and 17.3% lower than H167R. Effect size analysis indicated that an acidic environment exerted a stronger effect on H167-mediated Phe reduction than N under the conditions tested. Notably, in grains, the pH-specific mediation by H167 decreased Phe by 16.6% under acidic and N-deficient soil. This study provides a basis for mitigating Phe accumulation and associated PAH-related risks in rice through molecular strategies and soil pH and N management.
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